1. Field of the Invention
The present invention relates generally to the fields of monopropellants, hypergolic bipropellants, robotic actuators, and robotic power sources. More particularly, it concerns the use of a monopropellant or hypergolic bipropellant to power a robotic actuator. Even more particularly, the liquid fuels are utilized to generate gaseous products, which are in turn used to proportionally control the force or motion of a gas actuator.
2. Description of Related Art
A major concern facing those who design and build untethered mobile robots involves finding a suitable source of power and actuation for those robots. Note that unlike an engine, an actuator is characterized by controllable positive and negative power output across a bandwidth that typically spans from DC to several Hertz. Unlike tethered robots, untethered robots are not permanently connected to one or more power sources. Thus, untethered robots typically rely upon power that is carried upon the robot itself. The power supply most often used for untethered robots is battery power. Although battery power is effective in its own rite, it suffers from significant shortcomings.
Specifically, electrochemical batteries contain insufficient mass specific energy density to perform human-scale work for extended periods of time. For example, one of the more advanced current mobile robots—Honda's P-3 Humanoid Robot—has an operation time of only 15-25 minutes, depending on its workload. Operation times of this magnitude or smaller are not uncommon and represent one major technological roadblock for designing mobile robots that can operate remotely for extended periods of time. It should be noted that a trade-off generally exists between the mass-specific energy density and power density of current electrochemical battery technology. That is, batteries that provide relatively high energy densities typically suffer from relatively low power densities, and vice-versa. Therefore, though certain high energy density batteries do exist, they are generally incapable of providing the power required for human-scale mechanical tasks.
Electric motors are the most common type of actuator that would be used with batteries. For purposes of robotics, the peak mechanical power output of a motor is in a high speed and low torque regime, whereas robot motion is in a relatively low speed and high torque regime. Therefore, appropriate use of electric motors in robots generally requires a speed-reducing gearbox, which increases the size and weight of the actuation package.
An additional drawback to robotic actuation with electric motors is the fact that they consume electrical power in order to dissipate mechanical power. That is, robotic actuators must often absorb mechanical power from a load (e.g., lowering a payload under the influence of gravity). Rather than absorb that energy, an electric motor requires electric current for instantaneous control of torque, which in turn requires electrical power to dissipate mechanical power. Electric motors are therefore energetically expensive robotic actuators.
Hydraulic actuators can be used to transmit hydraulic power into mechanical power, but they require a source of hydraulic power. Hydraulic power must in turn be provided by a hydraulic pump, which is typically either electrically powered (i.e., battery powered) or fuel powered (i.e., gasoline or diesel engine powered). These systems are typically too heavy for human scale robots.
Internal combustion engines can also be used as a source of power for mobile robots. Such an engine cannot be used directly, since the output cannot be force or motion controlled over the bandwidths typically required of human-scale robots. An engine can, however, be utilized to drive a hydraulic or pneumatic pump or compressor to power a fluid-powered system, or alternatively to drive a generator to provide power for an electrically powered system. The added complexity of such systems, however, degrades the overall system energy density.
In view of shortcomings such as those outlined above, it is apparent that a better source of controllable power for use with untethered mobile robots would be desirable. This disclosure demonstrates that a better power and actuation source involves the use of monopropellants or hypergolic bipropellants. Although monopropellants (or hypergolic bipropellants) have been used as fuel-types in specialized applications, their potential has not been realized for use with untethered mobile robots until this invention.
U.S. Pat. No. 4,825,819 involves a fluid-powered actuator with a slidable piston. This patent essentially describes the operation of a bistable pilot-operated valve. Specifically, the valve draws from the primary fluid stream of fuel and oxidizer (or monopropellant) to switch a primary stream valve into either an on or off position. The actuator is therefore designed to move to one position or the other, and unlike the actuator described in this application, cannot provide proportional force or motion control. In other words, no disclosure is present to suggest how one can use monopropellants to continuously vary the output of one or more robotic actuators.
U.S. Pat. No. 5,992,700 involves an infusion device including a pressure containment pouch. In certain embodiments of the disclosure, gas is generated by drawing an aqueous solution of a peroxide or superoxide into an absorbent tablet that contains an enzyme or catalyst which promotes the decomposition of the peroxide or superoxide to decomposition products including oxygen gas. Although useful for applications such as medicine, this reference likewise does not disclose or suggest mechanisms whereby monopropellants may be used as a useful power source for untethered mobile robots.
U.S. Pat. No. 3,601,827 involves a self-contained underwater buoyancy system including a fuel tank containing a monopropellant fuel and a gas generator assembly that has a main body portion housing a catalyst bed that causes the monopropellant fuel to turn into a gas. The buoyancy system allows users to control buoyancy so that, a load of 1,000 pounds may be lifted at a depth of 150 feet. Although useful as applied to assisting underwater lifting, this reference does not disclose or suggest principles necessary to implement monopropellant power supplies in untethered mobile robots.
U.S. Pat. No. 5,932,940 involves a micro-gas turbine engine. The disclosure contemplates a wide range of propellant combinations, including monopropellants, such as hydrazine and hydrogen peroxide, which are preferably employed with the addition of a catalyst. This reference also does not disclose or suggest principles necessary to implement monopropellant power supplies in untethered mobile robots.
U.S. Pat. No. 3,581,504 involves a gas generator including an inlet for admitting a monopropellant. The disclosed gas generator provides a pressure-amplifying staged expansion cycle wherein relatively low pressure monopropellant is pumped by an impeller to a higher pressure. The monopropellant is then decomposed in the presence of a catalyst to produce a higher pressure exhaust gas. The disclosure states that a suitable monopropellant is hydrogen peroxide. Although useful to assist in techniques for pressure amplification, this reference does not disclose or suggest the applications discussed and claimed herein involving the use of monopropellants as power sources for robotics.
U.S. Pat. No. 5,807,011 involves a foot system for a walking robot. This disclosure describes a cylindrical connection member disposed at a center portion of the foot system for being connected to a leg system. It also describes a shock absorber supporting member and front and rear toes pivotally connected to an ankle member. Useful as particular robotic foot design, this reference, however, does not involve the use of monopropellants as power sources as discussed and claimed herein.
European Patent Application EP 0859143 involves a single stage monopropellant pressurization system wherein a monopropellant is stored within a tank. A gas generator supplied by the tank generates warm gas to pressurize other tanks. Disclosed monopropellants include hyrazine or monomethyl hydrazine or a combination of these fuels and possibly other additives such as water. Similar to the other references mentioned above, this reference does not disclose or suggest the technology discussed and claimed herein.
In summary, although conventional techniques may offer their own significant advantages, they, however, suffer from shortcomings as well. In particular, conventional technology does not disclose or suggest how to fully take advantage of monopropellant power sources. More particularly, conventional technology does not disclose or suggest how one could use monopropellant (or hypergolic bipropellant) sources of fuel to drive robotic actuators so that a more efficient, effective untethered mobile robot can be realized. The shortcomings of conventional technology, however, are addressed by the techniques disclosed and claimed below.